Terahertz Topological Insulators: Breaking Barriers for Future On-chip Wireless Communication

Terahertz (THz) wireless communication is a key enabling technology for sixth-generation (6G) and beyond, offering ultra-fast data rates, sub-millisecond latency, and high-capacity connectivity. THz on-chip communication is essential for realizing these benefits, supporting compact, high-speed, and energy-efficient intra/inter-chip data exchange through signal generation, modulation, and processing. However, practical deployment faces challenges such as scattering losses, low coupling efficiency, and degradation at sharp bends, limiting scalability and performance. Conventional THz platforms struggle to address these issues, highlighting the need for innovative solutions. Photonic topological insulators (PTIs) offer a transformative approach, using topologically protected edge states to enable backscatter-free, low-loss THz wave transport. Unlike traditional photonic platforms, PTIs offer intrinsic robustness to fabrication imperfections, structural defects, and environmental fluctuations, ensuring stable, high-efficiency signal transmission. Different classes of PTIs—Quantum Hall, Quantum Spin Hall (QSH), Floquet, and Quantum Valley Hall (QVH)—offer distinct trade-offs in nonreciprocity, integration complexity, and compatibility with complementary metal-oxide-semiconductor (CMOS) THz systems, with QSH and QVH PTIs particularly suited for passive robustness and scalable, low-loss network-on-chip (NoC) architectures. Beyond signal transport, PTIs offer additional functionalities critical to 6G on-chip systems—including nonreciprocal magnetless wave propagation, enhanced spectral efficiency in beamformers for spatially distributed users, ultrafast and miniaturized reconfigurable switching and power splitting, compact delay control, cellular-level on-chip sensing, efficient THz modulation, and programmable reconfigurability—while their CMOS compatibility, structural robustness, and energy-efficient operation through low-loss routing and thermally optimized, picojoule-per-bit transmission support scalable, low-cost deployment for adaptive, high-density NoC architectures. Integrating PTIs with low-loss photonic and electronic components enhances THz circuit performance, enabling advanced applications such as high-resolution imaging and sensing, biomedical diagnostics, adaptive routing, and secure on-chip communications. This review critically analyzes the impact of PTIs in addressing key limitations of THz on-chip communication, highlighting their potential to enable scalable, energy-efficient, and ultra-reliable wireless networks. PTIs also hold promise in quantum computing, neuromorphic computing, and analog in-memory processing, advancing next-generation information technologies.